The most commonly used black pigment is carbon black (C. I. Pigment Black 7). Carbon black is cheap and has excellent applications properties, such as light stability and weather stability, high colour strength, blackness, and neutral grey hues in a mixture with white pigments such as titanium dioxide (C. I. Pigment White 6), but also has serious disadvantages, such as problems with dispersibility of very fine particles, excessive electrical conductivity, and high absorption of near-infrared radiation (NIR) from the solar spectrum, which may lead to severe heating and possibly even to the destruction of the pigmented substrate or to the failure of the pigmented article.
In order to solve the problem, mixed metal oxides (MMO) have been proposed. While these oxides reflect the NIR radiation, their colour is weak and they contain heavy metals which are not unobjectionable for humankind and the environment.
There have also already been proposals of organic black pigments, such as C. I. Pigment Black 32, for example. Disadvantages shared by all known organic black pigments, however, are the fact that they are unsatisfactorily pitch-black (inadequate jetness) and that their hues in a mixture with white pigments are not a neutral grey but instead, depending on pigment, have a relatively strong tinge of colour, being tinged green, red, violet or brown, for example.
WO 00/24 736 discloses the compound of the formula
which is obtained by condensing the bisbenzofuranone of the formula
with isatin in acetic acid of unknown strength in the form of a violet powder (Example 12b). US 2003/0 083 407 complains that the yield is suspect. Moreover, no applications properties at all are disclosed, and the violet powder is in a highly aggregated form, whose dispersibility in plastics, for example, is entirely unsatisfactory.
WO 01/32 577 discloses glass-like materials, including (Example 41) a glass plate which is coated with tetraethoxysilane, aqueous nitric acid and the colorant of the formula
and which after heating to 200° C. has an absorption maximum at 760-765 nm.
Mixtures of organic colour pigments, which are likewise known, usually lead, like their individual components, to green-, red-, violet- or brown-tinged hues during the necessary dispersing step, since the individual components differ in their dispersibilities. Each dispersion method, therefore, requires extensive formulation work, and can subsequently no longer be changed rapidly as and when required—in actual practice, this is a disadvantage.
What remains, therefore, is the hitherto unfulfilled desire for heavy metal-free, jet-black pigments with high colour strength and good dispersibility, and also with very low conductivity and low absorption of near-infrared radiation.
WO 2009/010 521 is a patent application governed by Art. 54(3) EPC and Rule 64.3 PCT.
It has now been found, surprisingly, that, in a new, single-stage process, highly dispersible, strong, jet-black colorants (almost always pigments) having good fastnesses are obtained. In combination with basic additives, such as hindered amines (HALS) and/or UV absorbers of benzotriazole or triazine type, moreover, the physical durabilities which are obtained in plastics on weathering are, surprisingly, better than with known black pigments such as carbon black.